NOTE: end date changed to 05/15/2013 per HRP MTL dtd 11/11/11 (Ed., 11/18/11)

NOTE: change in start/end dates per JSC--now showing as 12/13/2007-12/17/2012 (previously 10/1/08-10/1/11)--2/2010

NOTE: Title change per JSC ; previous title: Evaluation of Maximal Oxygen Uptake (VO2max) During Long Duration International Space Station Missions (9/2009)

NOTE: Start/end dates changed per JSC (4/27/2009)

The specific aims of this research are:

1. To directly measure VO2max during and following long duration ISS missions.

2. To examine the current method of estimating VO2max change during and following ISS missions, establish if it can used to validly track actual measures of VO2max and, if indicated evaluate alternative methods of tracking changes in VO2max.

*- Exercise Physiology investigators will often refer to the maximum oxygen uptake value assessed in this study as “VO2peak” as repeated exercise tests are not used to verify the subject is truly at physiological maximum (not practical or even possible for certain time points of the study). For the purposes of this study and report, the investigators use the more familiar term “VO2max.”

Data reduction and analysis has been ongoing. A draft of an internal NASA report, outlining the primary findings of the study, has been submitted to the management of the Exercise Physiology and Countermeasures project at NASA-JSC. This report is also a preliminary draft of the final report due next month to the Human Research Program. The investigators are in the process of preparing manuscripts of the study findings that will be submitted to peer-reviewed scientific journals over the next few months.

The general findings of the study are:

1) Long duration ISS crewmembers typically experience a decline in peak oxygen uptake (VO2peak) which is evident within the first month of flight. VO2peak tends to slowly increase from the initially reduced levels during flight; however, the group data suggests that that VO2peak does not return to preflight levels. We speculate that the initial decrease in VO2peak is related to decreases in blood/plasma volume early in flight, and the upward trend following the initial decline is related to performance of in-flight exercise countermeasures. Immediately following flight, VO2peak is lower that preflight values, but recovers in the month following return to earth. The investigators note that there is a substantial amount of variation between subjects, with at least three subjects demonstrating no change during flight, however, the group data generally follows the description above.

2) The study data indicates that the method of using the heart rate (HR) response to submaximal exercise testing to track changes in VO2peak oftentimes conveys an erroneous impression of aerobic capacity, particularly when applied to an individual’s test results. This study objective was of particular interest to NASA Medical Operations because, although it generally recognized that maximal testing should provide the most accurate assessment of VO2peak, regular exercise tests being performed to maximal levels on ISS is undesirable for several reasons. These include the necessity of real-time ECG monitoring and down-link during maximal exercise tests conducted on ISS, which leads to resource constraints (both time and band-width constraints).

Using the submaximal exercise data collected during the VO2max study tests, estimates of VO2peak are calculated using the HR data and assuming the VO2 for each of the submaximal stages are similar those measured preflight [this is the method currently used for NASA Medical Operations]. The estimates of VO2max derived from this technique have varied from actual measurements of VO2max by as much as 40%. When actual measurements of submaximal oxygen uptake obtained during flight are substituted in the method described above, instead of assuming equivalence to preflight submaximal VO2 data, there is less variation from measured VO2peak but still the amount of variability seems inappropriately high to find utility as a method to accurately assess crew aerobic fitness.

3) The data obtained for ancillary physiologic measurements collected during the exercise tests (e.g. the non-invasive cardiac output measurements) are in the process of being statistically examined to determine if they have utility in developing a more accurate submaximal estimate of VO2peak.

NOTE: end date changed to 05/15/2013 per HRP MTL dtd 11/11/11 (Ed., 11/18/11)

NOTE: change in start/end dates per JSC--now showing as 12/13/2007-12/17/2012 (previously 10/1/08-10/1/11)--2/2010

NOTE: Title change per JSC ; previous title: Evaluation of Maximal Oxygen Uptake (VO2max) During Long Duration International Space Station Missions (9/2009)

NOTE: Start/end dates changed per JSC (4/27/2009)

The specific aims of this research are:

1. To directly measure VO2max during and following long duration ISS missions.

2. To examine the current method of estimating VO2max change during and following ISS missions, and establish if it can used to validly track actual measures of VO2max.

3. To determine if the addition of a non-invasive cardiac output measures during exercise will improve the accuracy of estimating changes in VO2max during and following ISS missions.

*- Exercise Physiology investigators will often refer to the maximum oxygen uptake value assessed in this study as “VO2peak” as repeated exercise tests are not used to verify the subject is truly at physiological maximum (not practical or even possible for certain time points of the study). For the purposes of this study and report, the investigators use the more familiar term “VO2max.”

The VO2max study continues to progress well. Seven subjects have now completed the study on board ISS, with the eighth currently on board. In addition, informed consent has been obtained for the remaining subject complement.

An internal NASA Mid-Study Review was conducted for the management of the Human Research Program (HRP) and the Human Health Countermeasures Element (HHC) in February, 2011. This review recommended continuing the study for the full complement of subjects.

The general interim findings of the study are:

1) Long duration ISS crewmembers typically experience a decline in VO2max which is evident within the first month of flight. VO2max tends to slowly increase from the initially reduced levels during flight; however, the group data suggests that that VO2max does not reach preflight levels. We speculate that the initial decrease in VO2max is related to decreases in blood/plasma volume early in flight, and the upward trend following the initial decline is related to performance of in-flight exercise countermeasures. Immediately following flight, VO2max is lower that preflight values, but recovers in the month following return to earth. The investigators note that there is a substantial amount of variation between subjects, with at least one subject demonstrating no change during flight, however, the group data generally follows the description above.

2) We continue to examine the accuracy of estimating VO2max, and tracking changes in VO2max, using the heart rate (HR) response to submaximal exercise. This study objective is of particular interest to NASA Medical Operations because, although it generally recognized that maximal testing should provide the most accurate assessment of VO2max, regular exercise tests being performed to maximal levels on ISS is undesirable for several reasons. These include the necessity of real-time ECG monitoring and down-link during maximal exercise tests conducted on ISS, which leads to resource constraints (both time and band-width constraints).

Using the submaximal exercise data collected during the VO2max study tests, estimates of VO2max are calculated using the HR data and assuming the VO2 for each of the submaximal stages are similar those measured preflight [this is the method currently used for NASA Medical Operations]. The estimates of VO2max derived from this technique have varied from actual measurements of VO2max by as much as 28%. Thus, it is highly likely that we will conclude that this technique in not a desirable one for Medical Operations to continue to utilize.

We also perform a similar calculation using the measured VO2 values for submaximal exercise, instead of assuming equivalence to preflight values. The differences from actual measurements of VO2max are reduced, with the maximal difference being approximately 14%. Thus, there is increased precision in using this technique but it still may be too variable to recommend for accurate assessment of aerobic fitness.

3) Ancillary measurements taken during the exercise tests (e.g. the cardiac output measurements) have been obtained. Determination of their utility in developing a more accurate submaximal estimate of VO2max is ongoing.

NOTE: change in start/end dates per JSC--now showing as 12/13/2007-12/17/2012 (previously 10/1/08-10/1/11)--2/2010

NOTE: Title change per JSC ; previous title: Evaluation of Maximal Oxygen Uptake (VO2max) During Long Duration International Space Station Missions (9/2009)

NOTE: Start/end dates changed per JSC (4/27/2009)

The specific aims of this research are:

1. To directly measure VO2max during and following long duration ISS missions.

2. To examine the current method of estimating VO2max change during and following ISS missions, and establish if it can used to validly track actual measures of VO2max.

3. To determine if the addition of a non-invasive cardiac output measures during exercise will improve the accuracy of estimating changes in VO2max during and following ISS missions.

*- Exercise Physiology investigators will often refer to the maximum oxygen uptake value assessed in this study as “VO2peak” as repeated exercise tests are not used to verify the subject is truly at physiological maximum (not practical or even possible for certain time points of the study). For the purposes of this study and report, the investigators use the more familiar term “VO2max.”

It is too early in the study to draw any conclusions from the findings to date. However, some preliminary observations are offered here:

1. The VO2max responses of the subjects during flight have been variable, with 2 subjects demonstrating declines >20%, 1 subject having a more modest decline (~10%) and one subject remaining unchanged from preflight levels.

2. There are differences observed between the estimates of aerobic capacity derived by submaximal test data (calculated using either HR and work rate data, or HR and submaximal VO2 data) and measured VO2max. The magnitude of this difference has been inconsistent when compared across subjects.

NOTE: change in start/end dates per JSC--now showing as 12/13/2007-12/17/2012 (previously 10/1/08-10/1/11)--2/2010

NOTE: Title change per JSC ; previous title: Evaluation of Maximal Oxygen Uptake (VO2max) During Long Duration International Space Station Missions (9/2009)

NOTE: Start/end dates changed per JSC (4/27/2009)

See also http://www.nasa.gov/mission_pages/station/science/experiments/VO2max.html

[Ed. note: added to Task Book in Feb 2009 when received information]